1. Field of the Invention
The present invention relates to a method of cleaning inside the processing chamber of CVD equipment used for semiconductor manufacturing. The invention particularly relates to a method of cleaning inside the processing chamber employing a remote plasma.
2. Description of the Related Art
In CVD (Chemical Vapor Deposition) equipment used for semiconductor manufacturing or deposition equipment including sputtering equipment, if deposition onto an object to be processed (e.g., a semiconductor wafer) is performed continuously, deposits adhere to internal walls of a processing chamber, etc. other than the object to be processed. When the deposits exfoliate, they cause particle contamination in a deposition process, resulting in wiring malfunction of devices such as DRAM or deposition failure. Consequently, it is required to clean inside a processing chamber with a given cycle.
Up to now, as disclosed in Japanese Patent Laid-open No.1994-97154, a method of bringing gas containing PFC (Perfluoro-compound) such as CH4, C2F6, C3F8, CHF3, SF6, NF3, etc. as cleaning gas into a reaction chamber, generating reaction active species (mainly fluorine radicals) by exciting the cleaning gas into plasma by applying high-frequency power to upper/lower electrodes, and removing deposits inside the reaction chamber by gaseous decomposition (in-situ cleaning) has been used.
In the case of the in-situ cleaning, however, because plasma is generated by applying high-frequency power to the upper electrode, which is used during a deposition process, ion collision is caused by charged particles generated in a space between the upper electrode and a susceptor which is the lower electrode. As a result, sputtering of a surface of the upper electrode is caused, resulting in problems such as by-product generation and electrode damage. Additionally, gaseous species containing PFC have an extremely high global warming potential (=infrared absorption factor x the duration of the atmosphere), long-range effects on the earth are feared.
To solve these shortcomings, a remote plasma cleaning method, in which plasma is excited outside a reaction chamber and cleaning gas is activated in the reaction chamber, was developed. In this method, NF3 is mainly used as cleaning gas; NF3 is dissociated and activated inside the remote plasma-discharge device; reaction active species generated in the device are brought into the reaction chamber to decompose and remove deposits adhering on inner walls, etc.
In the case of remote plasma cleaning, because plasma is generated outside the reaction chamber, only electrically-neutral atoms and molecules are brought into the reaction chamber and charged particles are not brought in. Consequently, because cleaning inside the reaction chamber is achieved only by chemical reactions, it is possible to prevent physical damage to electrodes.
On the other hand, because capacity inside the reaction chamber has been increasing as diameters of objects to be processed have become larger in recent years, removing deposits from inner walls, etc., which are remote from a plasma-generating area, becomes difficult and time required for cleaning tends to increase. If cleaning time increases, processing time per unit number of pieces of objects to be processed increases, directly leading to lowering of device throughput.
Additionally, as disclosed in Japanese Patent Laid-open No.1998-149989, if a plasma output value applied, which is used for a remote plasma cleaning discharge device, is in the range of 500 to 1500 W, supply gas is not decomposed completely. If supply gas not decomposed by plasma is discharged, there is the risk of having an adverse effect on the environment. Consequently, it is required to activate supply gas using approximately 3.0 to 12 kW output so that the supply gas is completely dissociated. In terms of device operational cost, however, effective cleaning using an output of 3.0 kW or lower is desired.
To solve these problems, accelerating cleaning rates and promoting efficiency accommodating large-capacity reaction chambers are required. The inventors of the present invention focused attention on cleaning gas, which had a decisive influence on promoting efficiency of cleaning. It is fluorine radicals that make a large contribution to reaction chamber cleaning, and increase in an amount of fluorine radicals to be generated is thought to directly lead to improvement of cleaning rates. It is not to say, however, that gas species whose amount to be generated is larger are simply good, but it is to say that gas species are dirable, which can dissociate deposits with less energy as compared with conventional NF3, etc. (i.e., an amount of fluorine radicals to be generated per unit energy is large) and with which gas cost calculated from a gas amount required per unit number of objects to be processed is low. A gas which can most satisfy these conditions is F2, which comprises two fluorine atoms. Gas cost per unit volume of this F2 gas is exceedingly less expensive as compared with NF3.
Consequently, the object of the present invention is to provide a remote plasma cleaning method for cleaning a reaction chamber of CVD equipment at high cleaning rates.
The second object of the present invention is to provide a remote plasma cleaning method with low cleaning operational cost and high efficiency.
The third object of the present invention is to provide a remote plasma cleaning method which is environmentally friendly and has least impact on global warming.